The invention relates to a write apparatus of an optical storage medium and, in particular, to an apparatus protecting a header region of the optical storage medium.
Digital Versatile Disc - Random Access Memory (DVD-RAM) is a disc specification which specifies rewritable DVD-RAM media and appropriated DVD writers. An optical disc with DVD-RAM format is divided into a plurality of sectors, each consisting of a write region and a header region. Each header region is embossed with physical information data (PID) therein. Overwriting is not allowed in the header region, or the physical information data (PID) may be damaged. Thus, it is necessary to stop recording before the header region of the next sector.
However, when data is written to the optical disc in DVD-RAM format, the data can be overwritten in the header region. When the duration of a write clock period is longer than it should be, data can be written in the header region of the next sector. As a result, the physical information data (PID) are damaged and the written user data cannot be retrieved.
U.S. Pat. No. 6,661,752 discloses a method of protecting a header region by detection thereof, as shown in FIG. 1. When the header region is detected, data recording is stopped and part of the encoded EFM data is not written through a laser diode. Thus, the unwritten data needs to be encoded again and written to another sector later. Alternatively, the write process may stop temporarily and restart after the write system is stabilized. According to DVD-RAM format, a buffer field of 25 bytes prvides redundancy in a sector of 2697 bytes. In other words, no error more than 1% is allowed. However, when the wobble quality of the optical disc is not good or rotation of a spindle is perturbed, variation of a write clock for header detection exceeds 1%. As a result, data recording is often interrupted when the header region is detected during data recording.